1. Field of the Invention
This invention relates to devices for recording non-electric signals and is more particularly concerned with seismoelectric signal recording devices.
2. Description of the Prior Art
Known in the art is a seismoelectric signal recording device which is used for mineral prospecting. This device comprises several electromagnetic receivers, each having a pair of metal spikes which serve as electrodes. Each receiver is equipped with an amplifier from which signals are fed to a recorder which is, for example, a mirror-galvanometer oscillograph (cf., for example, USSR Invention's Certificate No. 174,380, IPC.sup.3 G 01 V 11/00, published in "Otkrytia, izobretenia, promyshlennye obraztsy, tovarnye znaki" No. 17,1965, Device for Mineral Prospecting).
The receiving electrodes are pickups of electrical voltages induced by the electromagnetic radiation in the rock rather than pickups of the electromagnetic radiation itself.
Voltages to be recorded are seriously affected where current conducting objects, such as rails or pipes in air headings, occur in the vicinity of the receiving electrodes. Moreover, modern mines are packed with powerful electrical equipment and surrounding rock is full of substantial currents of the mains frequency and its harmonics, which fall into the frequency range of the device and affect its sensitivity.
In addition, an array of receiving electrodes having long, tens of meters, connecting wires is inherently a low-frequency system. In other words the frequency band received by the electrodes is limited to the first tens of kilocycles.
The recorder of the device uses photographic paper since it is a mirror-galvanometer oscillograph. This also limits the frequency band of recorded signals because this frequency band is restricted by the mechanical resonance frequency of the galvanometer which rarely reaches 10 kilocycles even in the best instruments of this type.
The mirror-galvanometer oscillograph used as a recorder is also a serious disadvantage of the device since it involves handling of light-sensitive materials, their chemical treatment and drying processes. Besides, the lengthy treatment of photographic materials affects the efficiency of the device.
Also known in the art is a device for recording seismoelectric signals, comprising several seismoelectric pickups which are electrodes, each pickup being equipped with an amplifier and a magnetic tape recorder connected to each amplifier. The device has a time mark generator connected to the magnetic recorder to record time marks thereon, a shot instant pickup and a control unit of the device (cf., for example, Razvedka i okhrana nedr, No. 4, 1973, Moscow, V. G. Smirnov et al. "Kvarts-G seismoelectric station, pp. 35-40).
The aforementioned device operates as follows.
Signals from the receiving pickups are amplified and supplied to respective inputs of the multitrack tape recorder. Other inputs of the tape recorder receive signals of the time mark generator and the shot instant pickup.
The tape transport is switched on prior to the explosion to start turning the magnetic tape loop whereon the information is recorded by means of a multitrack head.
Recording is started at the moment the signal from the shot instant pickup arrives and ends when the tape loop completes a full turn.
The known device is deficient in that it does not register signals whose frequency exceeds 20 kilocycles, the limitation being imposed by the capacity of the tape recorder. It should be remembered that higher frequencies carry the bulk of the useful information on ore bodies within the rock, their structure and mineral composition.
The difference between the amplitudes of signals within the frequency band up to 20 kHz and over 20 kHz can reach 30 dB and more. In consequence, when signals are recorded on a magnetic tape recorder whose dynamic range does not exceed 40 dB, the high-frequency portion of the spectrum can be lost.
The known devices for recording seismoelectric signals use a short-circuited wire loop as a shot instant pickup element which is placed in the explosive charge. The signal generated by the explosion when the loop is broken is registered by the pickup. Since the shot-firing machine, the charge and the seismoelectric recorder are connected by wire, the input of the recorder can receive, at the instant of explosion, a powerful signal which can damage the input circuitry of the device (cf., for example, Seismoelectric method of prospecting minerals using Kvarts-1 device" edited by V. K. Komarov, Leningrad 1974).
Also known in the art are devices for recording seismoelectric signals, wherein the shot instant pickup is a portable radio set. But such sets are difficult to make compatible with input circuits of the device. In addition they are not protected against the explosion.